Surgical cutting accessory with nickel titanium alloy cutting head

ABSTRACT

A cutting accessory ( 20 ) for use with powered surgical tools. The cutting accessory has a hub ( 28 ) for coupling the accessory to the output shaft of a handpiece. A drive shaft ( 26 ) formed of stainless steel or other relatively rigid material extends forward from the hub. A head ( 30 ) formed from nickel titanium alloy or other metal that is more flexible than the material forming the drive shaft is attached to the distal end of the drive shaft. The head is shaped to form the cutting edges of the cutting accessory. In some versions of the invention, intermediate sections ( 60 ) of the drive shaft are formed from the flexible metal or metal alloy.

FIELD OF THE INVENTION

This invention relates generally to a surgical cutting accessory that isused to cut tissue and, more particularly, to a surgical cuttingaccessory with a nickel titanium alloy cutting head.

BACKGROUND OF THE INVENTION

One component that is an integral part of many surgical tool systems isthe cutting accessory. This cutting accessory is a device that istypically attached to some sort of driving unit. Often, but not always,the driving unit is some type of handpiece that contains an electricallyor pneumatically driven motor. The cutting accessory is an elongatedmember that extends from the handpiece. The distal end of the cuttingaccessory, the end furthest from the surgeon, is shaped to define acutting head. In order to remove tissue, the surgeon actuates thehandpiece and applies the cutting head of the accessory to the tissue tobe removed. If the tissue being cut is bone, the cutting head is used toform a bore in the bone or to otherwise shape the bone.

Often cutting accessories are fabricated from stainless steel.Advantages of making an accessory out of this material are that it isrelatively economical to provide, the steel can be shaped to define thesharp cutting surfaces of the head, and it can also withstand the rigorsof post manufacture sterilization without physical degradation.

Nevertheless, there are some disadvantages associated with providingcutting accessories with cutting heads formed from steel. Specifically,steel is relatively rigid. Consequently, when a cutting accessory with asteel head is pressed against bone, the surgeon may have to preciselyhold the accessory against the bone so that it does not bendsignificantly relative to the longitudinal axis of the bore beingformed. If there is significant deviation from this axis, the cuttinghead may not be able to withstand the stress.

SUMMARY OF THE INVENTION

This invention relates to a new and useful surgical cutting accessory.In one version of the cutting accessory of this invention, the accessoryis provided with a shaft formed from stainless steel and a head formedfrom a metal that has more flexibility than the stainless steel. In somepreferred versions of this invention, the material from which the headis formed is a nickel titanium alloy. This head may be a drill tip, abur head or open ended tubular member that forms part of a tissuecutter. In alternative versions of this invention, the whole of thecutting accessory, its shaft and head, are formed from material that hasa greater degree of flexibility than stainless steel.

In still other alternative versions of the invention, a cuttingaccessory may have a shaft that comprises one or more sections of rigidmaterial like stainless steel and one or more sections of a moreflexible metal or metal alloy such as the nickel titanium alloy. In someembodiments of these versions of the invention, the shaft is formedsubstantially of steel, has a distal end neck formed of the moreflexible metal or metal alloy and a cutting head formed of steel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the claims. Theabove, and further features and advantages of the invention, areunderstood by reference to the drawings in which:

FIG. 1 is a plan and partially cutaway view of a surgical cuttingaccessory of this invention;

FIG. 2A is an exploded view of a cutting accessory;

FIG. 2B is a plan and partially cutaway view of the outer tube of thecutting accessory;

FIG. 3 is a plan view of the drive shaft and head of the cuttingaccessory;

FIG. 4 is a cross-sectional view of the drive shaft;

FIG. 5 is plan view of the cutting head of the inner tube;

FIG. 6 is a side and partial cross-sectional view of an alternativedrive shaft of this invention;

FIG. 7 is a side view depicting how the drive shaft of FIG. 6 is seatedin an outer tube, the outer tube being shown in cross-section; and

FIG. 8 is a partially cutaway view of the distal end of still anotheralternative cutting accessory of this invention.

DETAILED DESCRIPTION

FIGS. 1, 2A and 2B illustrate one surgical cutting accessory 20 of thisinvention. The particular accessory is a subchondral drill used to cutholes in bone that is surrounded by soft tissue. This particular type ofdrill is designed for use in an endoscopic surgical procedure in whichits elongated body is inserted into a portal formed in the body of thepatient. It should be understood that other cutting accessories aredesigned to perform other types of surgical procedures, includingnon-endoscopic, open cut procedures.

The depicted cutting accessory 20 has an outer tube 22 that, in thisversion of the cutting accessory, is sometimes referred to as aretractable housing. The proximal end of the outer tube 22, the endopposite the distal end, is coupled to an outer hub assembly 24. Theouter hub assembly 24 is used to releasably hold the cutting accessory20 to the handpiece with which it is used, (handpiece not illustrated).One such handpiece is sold by the Applicants' Assignee under thetrademark TPS 12K Shaver. Located within, and extending axially throughouter tube 22 and outer hub assembly 24, is a tubular drive shaft 26. Aninner hub 28 is attached to the proximal end of the drive shaft thatextends out of the outer hub assembly 24. The inner hub assembly isshaped to releasably engage with a motor coupling that is connected tothe motor drive shaft that is part of the handpiece with which thecutting accessory 20 is used. This inner hub 28 is coupled to thehandpiece so as to transfer the rotational movement of the handpiecedrive shaft to the accessory drive shaft 26. It should, of course, berecognized that this rotational movement may not, at all times, beunidirectional. Some cutting accessories, in some or all surgicalprocedures, are driven in an oscillatory movement pattern by thecomplementary handpiece in order to perform the desired surgicalprocedure.

A head 30 is attached to the distal end of the drive shaft 26. Head 30is the portion of the cutting accessory 20 that performs the tissueremoval function.

In the depicted version of the invention, the outer hub assembly 24 isprovided with a head piece 34 that is the most proximal portion of theouter hub assembly. The proximal end of head piece 34 is formed withsurfaces 36 against which coupling members integral with the handpiecebear. It should be understood that the actual surface geometries of theinner hub 28 and the head piece 34 are a function of the couplingassembly integral with the handpiece with which the cutting accessory 20is used. Exemplary surface geometries for these components are describedand illustrated in the Applicants' Assignee's U.S. Pat. Nos. 5,192,292,SURGICAL APPARATUS USEABLE FOR ARTHROSCOPIC SURGERY, issued 9 Mar. 1993;5,690,660, ARTHROSCOPIC CUTTER HAVING CURVED ROTATABLE DRIVE, issued 25Nov. 1997; and 6,007,556, SURGICAL IRRIGATION PUMP AND TOOL SYSTEM,issued 28 Dec. 1999, each of which is incorporated herein by reference.Again, it should be understood that these surface geometries are onlyexemplary and not limiting; the actual shape of the outer hub assembly24 and inner hub 28 will be a function of the handpiece with which thecutting accessory 20 is used.

The proximal end of the outer tube 22 is slidably disposed within theheadpiece 34. More particularly, as seen by FIG. 2, a collar 35 isfitted around the outer tube so as to extend forward from a positionlocated forward of the proximal end of the tube. Collar 35 is the actualcomponent that slidably abuts the inner wall of head piece 34. Collar 35is further formed to define an annular lip 38 around its distal end.

The portion of the collar 35 that extends forward from the distal end ofhead piece 34 is encased within a cylindrical shell 40 also part of theouter hub assembly. Shell 40 is secured to head piece 34. A coil spring42 is disposed in shell 40 and extends around collar 35. One end ofspring 42 bears against the ring-shaped, distally directed face of thehead piece 34. The opposed end of spring 42 seats against collar lip 38.Spring 42 thus places a force on the collar 35 and outer tube 22 so asto push these components outwardly, away from head piece 34.

Inner hub 28, as discussed above, is shaped to engage with the driveintegral with the handpiece with which the cutting accessory 20 is used.The inner hub is also shaped to have a port 37 that is in communicationwith the center bore that extends axially through the drive shaft 26.Typically, the handpiece with which the cutting accessory 20 is used hasa bore that extends from the opening in which the accessory hubs 24 and28 are seated. A suction is drawn through this bore from a pump externalto the handpiece so as to draw a suction through the drive shaft 26.

In the depicted version of the invention, drive shaft 26, as seen inFIGS. 3 and 4, is formed so as to have a constant diameter main section47 that comprises approximately 60 to 90% the total length of the shaft.In more preferred versions, main section 47 comprises between 70 to 80%of the overall length of the shaft. After the constant diameter mainsection 47, the drive shaft has an inwardly tapered section 48. Anopening 50 is formed in tapered section 48. Opening 50 is the port inthe cutting accessory through which fluid and debris at the surgicalsite are drawn into the drive shaft 26. Drive shaft 26 is further formedso as to have a constant diameter neck 52 that extends forward from thedistal end of tapered section 26. In preferred versions of theinvention, drive shaft 26 is manufactured from stainless steel. One typeof stainless steel from which the drive shaft may be manufactured is 300Series stainless steel. In some versions of the invention, 304 Seriesstainless steel has proven to be a suitable material for forming thedrive shaft 26.

The drive shaft may be shaped to form the tapered section 48 and neck 52by a swaging process. In some versions of the invention, the drive shaft26 main section 47 has an outer diameter of 0.250 to 0.080 inches and awall thickness of 0.030 to 0.005 inches. For example, some versions ofthe invention are further formed so that the drive shaft main sectionhas an outer diameter of between 0.10 and 0.15 inches and a wallthickness of between 0.010 and 0.015 inches. It should also beunderstood that the metal or metal alloy from which the drive shaft isformed is relatively inflexible, for example, a metal or metal alloythat, when exposed to 1% or more strain, experiences plasticdeformation.

Head 30 is seated in the open end of drive shaft neck 52. The head isformed from a material that has a greater degree of flexibility than thematerial forming the drive shaft. For example in some preferred versionsof the invention, the head is formed from nickel titanium alloy. Analloy suitable for forming head 30 may be composed of the followingmaterials by weight percent: nickel 54.5 to 57.0%; oxygen (max) 0.05%;carbon (max) 0.07%; and the remainder titanium. Often, this particulartype of alloy is referred to as Nitinol. More generally, the metal ormetal alloy from which the head is formed is of sufficient flexibilitythat even when it is exposed to at least 3% strain it will recover itsinitial shape. More preferred metals and metal alloys from which thehead is formed are of sufficient flexibility that, when exposed to atleast 5% strain, the head will recover its initial shape.

Head 30 as seen in FIG. 5 is shaped to have a generally cylindricalshape. The head is further shaped to have opposed flats 54 that extendrearwardly from the proximally facing face of the head. The distal end56 of the head, the tip of the head, is formed in the shape of afour-sided pyramid that meets at a point. Flats 58 extend from two ofthe opposed diametrically opposed sides of the pyramid a short distanceproximally along the length of the head. The edges along which the sidesof the pyramid 56 meet are the cutting edges of the head 30.

After the drive shaft 26 is formed, head 30 is seated in the open endedneck 52. The material forming neck 52 is pressed against the proximalend of the head to compression secure the head in place. The neck ispressed against flats 54 so as to prevent the head from rotatingrelative to the drive shaft 26.

The drive shaft-and-head subassembly is fitted in the outer hub-outerhousing subassembly as seen in FIG. 2B. In many versions of theinvention, outer tube 22 and drive shaft 26 are dimensioned so that,absent any external force, the distal end of the outer tube just coversthe distal end of the cutting head.

The described cutting accessory 20 is employed to bore a hole in hardtissue, bone. The accessory is used by pressing its distal end againstthe bone at the location at which the bore is to be formed. Thehandpiece to which the accessory is attached is actuated to cause therotation of drive shaft 26 and head 30. The head 30 thus drills out thebone to form the desired hole. In this particular cutting accessory, theouter tube is disposed against the surface of the bone being cut. Theouter tube 22 thus serves as a guard to prevent soft tissue fromwrapping around the head 30 as the head is pressed into the bone. Owingto the telescoping relationship between the outer tube 22 and the outerhub assembly 24, the outer tube remains in a static position over thehole formed in the bone as the head 30 is pressed into the bone.

An advantage of the cutting accessory 20 of this invention is that thecutting accessory has a degree of flexibility at the location where itis needed, its distal end, its head end, and is otherwise relativelyrigid. Thus, during surgery, when the head 30 is used to bore into bone,if the accessory 20 is angled so as to be offset from the longitudinalaxis of the bone bore, since the head 30 is formed from a relativelyflexible metal alloy, it will bend while in the bore. Since the head 30bends, there is a significantly reduced likelihood that it or the driveshaft 26 will fail.

Still another advantage of this invention is that, if the cuttingaccessory 20 is subjected to side loading or bending when pressedagainst bone, the majority of the bending occurs in the head.Consequently, there is little, if any, bending of the shaft main section47. This reduction in drive shaft bending reduces both the degree andfrequency with which the bending of the drive shaft 26 is bent againstthe adjacent inner wall of the outer tube 22. The minimization of thedrive shaft-against-outer tube contact reduces the instance in whichsuch contact inhibits the rotation of the drive shaft 26.

Thus, the cutting accessory 20 of this invention is designed to flex atits distal end so as to not malfunction if angled while being used andto otherwise remain rigid so that the flexing does not adversely affectits use.

Still another advantage of the cutting accessory is that only arelatively small portion of the accessory is formed from the relativelyexpensive nickel titanium alloy. Thus, the cutting accessory of thisinvention is not appreciably more expensive than other cuttingaccessories.

It should be realized that the foregoing description is directed to oneparticular cutting accessory of this invention. Other versions of thisinvention may have features that are different from the describedcutting accessory. For example, in some versions of the invention, thehead may not be simply formed to function as a bore-forming drill. Insome versions of the invention, the head may be formed to have a stemwith a first diameter. This is the portion of the head that is securedto the drive shaft 26. Extending distally from the stem, the head 30 isformed to have a head member that has a second diameter that is greaterthan that of the stem. This head member has either a spherical or barrelshape. The head member is formed to have a number of different cuttingedges and thus functions as a bur. These burs are designed toselectively remove tissue against which they are pressed.

Also, there is no requirement that all versions of the invention beconstructed as drills or burs. In some versions of the invention, thehead may be shaped to form part of a cutter. That is, the head is in theform of a tube that is closed at its distal end that, proximally to theclosed distal end, has a window that is defined by sharp edges of thematerial forming the head. The outer tubes of the cutting accessories ofthese versions of the invention are formed with similar closed distalends and adjacent windows. The edges of the rotating cutting headcooperate with similarly sharp edges of the static outer tube tofunction as scissors that separate the tissue against which the distalend of the cutting accessory is pressed. The separated tissue is drawnby suction away from the surgical site through the window formed in therotating cutting head and the hollow center space within thecomplementary drive shaft. In these, as well as other versions of theinvention, it should be understood that the drive shaft of the cuttingaccessory may have constant outer diameter along the whole of itslength.

For example, while the described cutting accessory 20 is designed as asingle use disposable cutting accessory, other cutting accessories maybe designed to withstand the rigors of sterilization so that they can beused in multiple surgical procedures.

While one particular head 30 has been illustrated and described, otherversions of the cutting accessory of this invention may have heads withdifferent geometries. For example, other heads may not have thedescribed pyramidal shaped distal end. The ends of these heads could berounded. Similarly, grooves may be formed in the heads to providepathways for the material removed by the cutting edges of the heads totravel out of the bore being formed. Also, it should be recognized thatthe number of cutting edges with which the head is provided might varyfrom what has been described. Furthermore, there is no requirement that,in all versions of the invention the cutting edges have a linear shape.In still other versions of the invention, these cutting edges may havecurved, spiral or helical shapes.

In still other versions of the invention, the material of increasedflexibility is not located at the head. FIGS. 6 and 7 illustrate onesuch version of this invention. Here, the drive shaft 26 a has a mainsection 47 a formed of stainless steel. A tubular member 60 formed fromthe more flexible Nitinol is secured to the distal end of main section47 a. In order to facilitate the mating of these two components, thedistal end of the main section 47 a has a small forward facing lip 62that seats in a circumferential groove 64 formed around the proximalfacing face of member 60 adjacent the inner wall of the shouldersection. The components 47 a and 60 are then joined together.

A shoulder section 66 formed from stainless steel extends forward fromtubular member 60. Shoulder section 66 is shaped to define taperedsection 48 a and neck 52 a. A head 30 a formed of stainless steelextends forward from neck 52 a. A lip-in-groove assembly similar to thatused to secure member 60 to main section 47 a is employed to mate member60 with shoulder section 66.

In this version of the invention, the drive shaft 26 a is encased withinouter tube 22 a. Outer tube 22 a is formed so that the portion of thetube 22 a that subtends relatively flexible tubular member 60 has aninner wall 68 with a diameter greater than that of the diameter of theinner wall that surrounds the rest of drive shaft 26 a.

If the above described version of the invention is subjected to sideloading, then member 60 will be the primary member that flexes. Sincethere is a relatively wide interstitial gap between the outer surface ofmember 60 and the adjacent outer tube inner wall 68, the likelihood ofcontact between these two surfaces is relatively minimal. Thus, thisversion of the invention is constructed so that a relatively rigid,efficient cutting surface can be pressed against the tissue. The driveshaft 26 a will flex if there is significant side loading so as to avoidfailure of this component or the actual cutting head, and in the eventthere is flexing of the drive shaft, there will be minimal contactbetween the drive shaft and the outer tube 22 a that can inhibitrotation of the drive shaft.

It should, of course, be realized that in other versions of theinvention, the member formed of the more flexible metal or metal alloymight not always form the most distal end portion of the drive shaft. Instill other versions of the invention, this flexible member may form theportion of the drive shaft that extends from the inner hub.Alternatively, this flexible member may be located at or near the centerof the drive shaft. Also, some versions of the invention may have two ormore flexible members that form different portions of the drive shaft.

In one or more of the above-described versions of the invention, theindividual sections of the drive shaft formed out of the rigid metal ormetal alloy may not be physically separate units. In these versions ofthe invention, one or more small spaced apart webs may extend from theindividual sections of the rigid material. These webs are shaped so asto inscribe a circle that has an outer diameter less than the outerdiameter of the drive shaft with which they are integral. Once thisportion of the drive shaft is formed, bands of the flexible metal ormetal alloy are wrapped over each set of webs. These bands thus seal theinside of the drive shaft and provide further means for transferring thetorque developed by the drive shaft to its distal end sections.Alternatively, instead of employing webs integral with the workpiecefrom which the drive shaft rigid sections are formed to interconnectthese sections, wire or braid may perform this function. Again, in theseversions of the invention, the bands of flexible metal both seal thedrive shaft and further transfer the rotational movement of the proximalend of the shaft to the distal end.

In order to perform the above-described torque transfer function, therigid and flexible sections of the material forming the drive shaft maybe formed with interlocking teeth.

An alternative cutting accessory of this invention may be a bent angleaccessory 70 the distal end of which is depicted in FIG. 8. Cuttingaccessory 70 has a tubular housing 72 that, either during manufacture orpost manufacture is bent at a particular angle. Internal to the housing72 is a drive shaft 74. Drive shaft 74 has a tubular proximal section 76formed of the relatively inflexible metal or metal alloy. A band orsleeve 78 formed of the more flexible metal or metal alloy is joined tothe distal end of section 76. Sleeve 78 is located in the portion ofhousing 72 that is angled. A drive shaft distal end section 80 is joinedto the distal end of sleeve 78. A cutting head, a spherical shaped bur82 being illustrated by way of example, is attached to the distal end ofdrive shaft distal end section 80.

Cutting accessory 70 is thus constructed so that sleeve 78, whileflexible, is able to transmit torque between the drive shaft sections 76and 80 and define a portion of the conduit through which suction fluidis drawn towards the proximal end of the cutting accessory. (Proximalend of cutting accessory 70 not shown.) In still other versions of theinvention, plural sleeves 78 can be employed to function as the flexibletorque-transmitting, conduit-defining members desirable in a bent angledcutting accessory.

Also, in some versions of the invention, it may be desirable to makethis flexible section solid. In these versions of the invention, theflexible section is most often located immediately proximal to theactual cutting head. Immediately proximal to this flexible section, thedrive shaft is formed with an opening through which fluid and debris aredrawn from the surgical site.

Similarly, while the drive shaft of the disclosed version of theinvention is formed with a window and is hollow so as to allow a suctionto be drawn therethrough, there is no requirement that all versions ofthe invention be so configured. Furthermore, while it is anticipatedthat in most versions of the invention, the head will be solid along itslength, this need not be a requirement for all versions of theinvention. In some versions of the invention the head may be formed withone or more bores. These bores communicate with the center hollow spaceof the drive shaft to facilitate the drawing of a suction flow throughthe head.

Also, there is clearly no requirement that all versions of the cuttingaccessory of this invention have the described outer tube. Just as thereis no requirement that the cutting accessory have an outer tube, thereis no requirement that, all versions of the invention that are providedwith an outer tube have the described mechanism for telescopicallyretracting the outer tube as the drive shaft and head are pressed intotissue.

It should further be understood that the metals and/or metal alloys fromwhich the drive shaft 26 or 26 a the head 30 or 30 a and member 60 ofthis invention are formed may be different from what has been described.Also, the components of this cutting accessory may be formed fromdifferent combinations of material than has been described. For example,it may be desirable to form a cutting accessory with the flexible member60, the distal end of the drive shaft with steel, and a head formed fromNitinol or other metal or metal allow that has a greater flexibilitythan the steel.

Moreover, when the flexible metal/metal alloy is used to form a portionof the drive shaft, means different from what has been described may beused to secure together the sleeves of different material thatcollectively form the drive shaft. For example, these components may beprovided with complementary beveled proximally and distally directedsurfaces that facilitate their mating. Alternatively, these componentsmay be provided with complementary proximally and distally directedteeth that engage each other.

Thus, it is the object of the appended claims to cover all suchvariations and modifications that come within the true spirit and scopeof this invention.

1. A surgical cutting accessory, said cutting accessory comprising: adrive shaft having opposed proximal and distal ends, said drive shaftbeing formed from a metal or metal alloy that has a first degree offlexibility; a first hub integral with the proximal end of said driveshaft, said first hub being shaped to couple said drive shaft to amotor; and a head attached to the distal end of said drive shaft torotate in unison with said drive shaft, said head having a tip that isshaped to have at least one cutting edge, said head being formed from ametal or metal alloy that has a second degree of flexibility, the seconddegree of flexibility being greater than the first degree offlexibility.
 2. The surgical cutting accessory of claim 1, wherein: saiddrive shaft has a tubular shape so as to have a hollow space and isformed with a window adjacent the distal end of said drive shaft; andsaid first hub is shaped to have an opening that is in communicationwith the hollow space within said drive shaft.
 3. The surgical cuttingaccessory of claim 1, wherein said head is formed to have a solid stemthat is secured to said drive shaft.
 4. The surgical cutting accessoryof claim 1, wherein said head is formed so that the portion of said headthat extends from said drive shaft to said head has a constant diameterand said tip has a diameter less than the diameter of the constantdiameter portion.
 5. The surgical cutting accessory of claim 1, furtherincluding: an outer tube disposed over said drive shaft, said outer tubehaving opposed distal and proximal ends; and a second hub attached tothe proximal end of said outer tube.
 6. The surgical cutting accessoryof claim 1, wherein: said drive shaft is formed from a metal or metalalloy that, if exposed to 1% or more strain, experiences plasticdeformation; and said head is formed from a metal or metal alloy that,when exposed to at least 3% strain, will retain the initial shape ofsaid head.
 7. The surgical cutting accessory of claim 1, wherein: saiddrive shaft is formed from a metal or metal alloy that, if exposed to 1%or more strain, experiences plastic deformation; and said head is formedfrom a metal or metal alloy that, when exposed to at least 5% strain,will retain the initial shape of said head.
 8. The surgical cuttingaccessory of claim 1, wherein said head is formed from a nickel titaniumalloy.
 9. A cutting accessory, said cutting accessory comprising: afirst hub shaped to engage a motor; an accessory drive shaft that isattached to said first hub to rotate in unison with said first hub, saiddrive shaft extending forward from said first shaft and having a distalend that is spaced from said first hub, wherein said drive shaft isformed from steel, the steel having a first degree of flexibility; and ahead, said head having a stem that is attached to and extends from thedistal end of said drive shaft and secured to said drive shaft to rotatein unison with said drive shaft and a tip located forward of said driveshaft, said tip formed with at least one cutting edge, wherein said headis formed from a metal or metal alloy that has a second degree offlexibility, the second degree of flexibility being greater than thefirst degree of flexibility.
 10. The surgical cutting accessory of claim9, wherein: said drive shaft has a hollow tubular shape and is formedwith a window adjacent the distal end of said drive shaft; said firsthub is shaped to have an opening that is in communication with thehollow space within said drive shaft; and said stem of said head issecured to said drive shaft at a location distal from where the windowis formed in said drive shaft.
 11. The surgical cutting accessory ofclaim 9, wherein said head is formed so that said stem has a constantdiameter and said tip has a diameter less than the diameter of saidstem.
 12. The surgical cutting accessory of claim 9, wherein: said driveshaft is a tubular shaft with a hollow center space and is shaped tohave a main section with a first constant diameter that extends distallyfrom said first hub, a tapered section with decreasing diameter locatedat a distal end of said main section, a window formed at least partiallyin said tapered section, and a neck that extends forward from saidtapered section; said first hub is formed with an opening that is incommunication with the hollow space of said drive shaft; and said stemof said head is fitted in said neck of said drive shaft.
 13. Thesurgical cutting accessory of claim 9, wherein: the steel from whichsaid drive shaft is formed from a metal or metal alloy that, if exposedto 1% or more strain, experiences plastic deformation; and said head isformed from a metal or metal alloy that, when exposed to at least 3%strain, will retain the initial shape of said head.
 14. The surgicalcutting accessory of claim 9, wherein said head is formed from a nickeltitanium alloy.
 15. A cutting accessory, said accessory comprising: afirst hub, said first hub shaped to interlock with the output couplingof a motor to rotate in unison with the output coupling, said first hubshaped to have an opening; a drive shaft formed of steel and having ahollow tubular shape that is secured to said first hub to rotate inunison with said first hub, said drive shaft shaped to have a mainsection with a first constant diameter, a tapered section at a distalend of said main section of decreasing diameter, a neck at the distalend of said tapered section that has a second diameter less than thefirst diameter wherein said drive shaft has a center space that is incommunication with the opening of said hub and is further formed to havea window that is at least partially located in said tapered sectionwherein, the steel forming said drive shaft has a first degree offlexibility; and a cutting head formed from a metal or metal alloy, saidcutting head having: a stem that is secured in said neck of said driveshaft so that said cutting head rotates in unison with said drive shaft;and a tip located at the distal end of said cutting head, said tipshaped to form at least one cutting edge wherein, the metal or metalalloy from which said cutting head is formed has a second degree offlexibility, the second degree of flexibility being greater than thefirst degree of flexibility.
 16. The cutting accessory of claim 15,wherein the portion of said stem of said cutting head that extends fromsaid drive shaft to said tip has a diameter and said tip has an outerdiameter less than the diameter of the constant diameter portion of saiddrive shaft.
 17. The cutting accessory of claim 15, wherein the portionof said stem of said cutting head that extends from said drive shaft tosaid tip has a constant diameter.
 18. The cutting accessory of claim 15,further including: an outer tube disposed over said drive shaft, saidouter tube having opposed distal and proximal ends; and a second hubattached to the proximal end of said outer tube.
 19. The cuttingaccessory of claim 18, wherein said outer tube is attached to saidsecond hub so that said outer tube is able to move longitudinallyrelative to said second hub.
 20. The surgical cutting accessory of claim15, wherein: the steel from which said drive shaft is formed from ametal or metal alloy that, if exposed to 1% or more strain, experiencesplastic deformation; and said head is formed from a metal or metal alloythat, when exposed to at least 3% strain, will retain the initial shapeof said head. 21-29. (canceled)